A failing transformer isn’t just a technical issue; it’s a high-stakes problem. Transformers support the backbone of industrial and utility power distribution, and any malfunction can mean costly outages, equipment damage, or even fire hazards. The average cost of repairing a transformer that has failed is in the tens of thousands of dollars, and the outage could leave thousands of people without electricity. Maintenance of these devices is therefore mission-critical.
The current gold standard is proactive monitoring and condition-based maintenance, which substitutes time-based checks that are outdated with data-based diagnostics. The most promising and non-destructive of these has been infrared thermography as an early detector of faults.
Common Transformer Failure Modes
To detect problems early, it’s crucial to understand the common failure modes of transformers:
1. Loose or Corroded Electrical Connections
Loose bolts or oxidized contacts increase resistance, causing localized heating. This can damage bushings or connection terminals.
2. Overheating
Often caused by load imbalances, blocked radiators, or restricted airflow. Persistent overheating can degrade insulation or trigger gassing.
3. Oil Degradation or Contamination
In oil-filled transformers, dirty or low oil levels impair cooling and can lead to dangerous pressure build-ups or arcing inside the tank.
4. Insulation Breakdown
Age or environmental factors like moisture degrade insulation, leading to electrical discharge and internal shorts.
5. Partial Discharges and Corona
Localized ionization (partial discharge) in high-voltage parts can erode components and trigger long-term failure.
These modes are often invisible to the naked eye until too late—which is why predictive diagnostics are so essential.
Predictive Maintenance Approaches
Predictive maintenance relies on monitoring the actual condition of equipment to anticipate failures. When it comes to transformers, several tools can be used:
- Infrared Thermography (IR): Detects abnormal heat patterns.
- Dissolved Gas Analysis (DGA): Identifies gassing patterns in oil, indicating arcing or thermal breakdown.
- Ultrasound & Acoustic Emissions: Detect arcing or internal mechanical stress.
- Electrical Testing: Includes turns ratio tests, insulation resistance, and sweep frequency response analysis.
- Visual Inspection: Regular checkups of the physical condition, gauges, and connection points.
While each tool has its strengths, infrared thermography stands out for its speed, affordability, and ability to inspect energized equipment.
Infrared Thermography in Transformer Inspection
Infrared thermography is based on capturing the heat radiation of surfaces. The infrared cameras can be used to find such abnormalities since the faulty electrical or mechanical connection can produce more heat as it has a higher resistance or friction.
What It Detects:
- Load Imbalances
- Loose or corroded terminals
- Overheating windings or LTCs (Load Tap Changers)
- Low oil levels or blocked radiators
Benefits:
- Non-contact and non-invasive
- Fast, with real-time data
- Safe, can be done while energized
- Cost-effective for routine checks
Best Practices:
- Perform scans under full load conditions for meaningful data.
- Ensure proper camera calibration.
- Account for ambient temperature and wind, which can affect surface readings.
According to ThermoElite, infrared inspection is particularly effective in oil-filled transformers for spotting blocked cooling tubes or overloaded bushings. They report that infrared scans have saved multiple units by detecting low oil levels in time for corrective action (ThermoElite, 2025).
Case Studies & Real-World Applications
Case 1: Avoiding Core Exposure with infrared
In ThermoElite, an inspection in 2017 revealed that the radiator fins were abnormally cool, which was an indication of low oil levels. The scan repeated after the addition of 80 gallons of oil had the normalization of temperatures, preventing what would have probably been a disastrous failure (ThermoElite, 2025).
Case 2: Saving a Transformer via Tap Changer infrared
An IRINFO.org case from PSEG describes a high LTC (Load Tap Changer) temperature anomaly. Further inspection revealed carbonized oil and rust. By cleaning and refilling the LTC, the lifespan of the transformer was extended significantly (Infrared Training Center, 2025).
Return On Investments (ROI)
| Scenario | Cost Estimate | Outcome |
| Thermographic Inspection (Routine) | $300 – $800 per unit | Early issue detection, no shutdown needed |
| Transformer Failure (Minor Repair) | $5,000 – $15,000 | Parts replacement, labor, short outage |
| Transformer Failure (Major) | $40,000 – $100,000+ | Extended downtime, equipment damage, possible fire risk |
| Unplanned Downtime (per hour) | $10,000+ (industrial avg) | Revenue loss, staff idle, emergency response |
| Replacement Transformer (New Unit) | $50,000 – $250,000 | Lead time delays, installation costs |
The cost of a single thermographic inspection is a fraction of the potential repair and outage costs. For utilities, the ROI is clear: less downtime, lower repair costs, and extended asset life.
Example: Thermographic Survey Report (Condensed)
Apparatus Testing and Engineering, Inc. performed a thermographic survey on one MV transformer for American Commodity Company in Williams, CA (July 17, 2025). The purpose was to detect electrical discrepancies before failure.
Findings:
- X3 bushing measured 8°C higher than X1 and X2 phases under equal load, indicating a likely poor internal connection.
- Transformer operating at 58°C with max of 73°C during scan.
- No other thermal issues observed.
Recommendations:
Perform NETA-recommended maintenance testing on July 23, 2025 to confirm and address the issue. Repair priority: Medium.
Repair Guidelines (Simplified):
- 1–3°C rise: Possible deficiency, monitor.
- 4–15°C rise: Probable deficiency, repair at next maintenance.
- 16°C rise: Major discrepancy, repair immediately.
Limitations & Complementary Techniques
Infrared thermography is powerful—but not perfect.
What Infrared Can’t Detect:
- Internal gassing or oil contamination
- Moisture inside insulation
- Micro-cracks or chemical degradation
- Hidden internal short circuits
Complementary Tools:
- Use DGA to detect gas buildup from arcing or overheating.
- Use ultrasound to listen for arcing or corona not visible thermally.
- Electrical tests can confirm insulation strength or winding problems.
Pro Tip:
Capture baseline infrared images under known good conditions. These serve as references to track anomalies over time.
Conclusion & Recommendations
Maintaining transformer health is a high-stakes job but not an impossible one. With the right tools and strategies, maintenance teams can spot issues before they turn critical.
Key Takeaways:
- Know transformer failure modes in order to inspect.
- Apply infrared thermography as a frontline method of visualization of thermal anomaly.
- Use infrared scans in combination with DGA, acoustic, and electrical diagnostics.
- Under load inspection should always be conducted, tools should be calibrated, and environmental awareness maintained.
- Make in-depth thermal records and baseline images to observe long-term changes.
The more active you are in maintaining your equipment, the longer your equipment will serve you and the fewer outages or disasters you will have to deal with. Want to improve your transformer health program? Download our free Infrared Inspection Guide or book a thermal inspection with our certified thermographers today.
